(a) Technical Field of the Invention
The present invention relates to an oar for rowboat and more particularly, to such an oar, which is equipped with a pivoted supplementary blade to enhance the rowing.
(b) Description of the Prior Art
When rowing a rowboat, an oar or two oars shall be used. An oar for this purpose comprises a shaft, a grip fixedly provided at one end of the shaft, and a flat blade fixedly provided at the other end of the shaft. For comfortable gripping of the hand, the grip of an oar is made in a cylindrical shape. When rowing a rowboat, the user who sits in the rowboat must insert the blade of the oar into the water and then move the oar to force the blade against the water, and then lift the oar from the water, and then repeat the rowing procedure again and again. When forcing the blade against the water, a resisting force is produced to move the rowboat on the water.
A person who learned fluid mechanics or mechanics knows that the wider the area of the water expelling surface of an oar is the greater the water resisting force will be, i.e., an oar having a relative bigger blade surface area can move the rowboat on the water more quickly. However, it requires much effort to row an oar having a relatively greater blade surface area.